Long term decomposition and crystallisation kinetics of ADN under some crystallographic aspects

Abstract. Ammonium dinitramide [NH4]+[N3O4]- (ADN) is a very promising replacement for the chlorine bearing oxidizer ammonium perchlorate, avoiding large scale hydrochloric acid release as well as a strong spectroscopic signature. Understanding the responsible mechanisms for the long- and short term decomposition processes requires the investigation of the crystal structure, the crystal growth and its resulting habitus as well as the thermal decomposition processes. Ammonium dinitramide obtained from aqueous solutions was investigated. Applied methods include in-situ PXRD, long term PXRD investigations, DSC, SEM, spectroscopy and in perspective in-situ single crystal diffraction experiments. The investigations suggest that decomposition reactions result in crystal cleaving along (020) planes, which are energetically unfavorable faces of slow growth. The proposed mechanism in question combines aspects of acidity, thermal stress and vacuum stability. A significant factor is the presence or absence of ammonia and acids to inhibit decomposition reactions NH4+ -> NH3 ↑+ H+ triggering H+ + N3O4- -> HNO3 + N2O ↑ and HNO3 + NH4N3O4 -> NH4NO3 + H+ + N3O4-. Understanding the mechanism of decompositions helps to improve the fabrication of ADN-based fuels, avoiding potentially harmful treatment. Avoiding perchlorate caused environmental and detectability issues is of great concern for rocket applications.